Bianca E. Nelson

The benefits of ultrashort optical pulses in optically interconnected systems

Many properties of an optically interconnected system can be improved through the use of a modelocked laser. The short pulse duration, high peak power, wide spectral bandwidth, and low timing jitter of such a laser lead to these benefits. Timing advantages include simplified synchronization across large chip areas, receiver latency reduction, and data resynchronization. Lower power dissipation may be achieved through improved receiver sensitivity. Additional applications of short optical pulses include time-division multiplexing, single-source wavelength-division multiplexing, and precise time-domain testing of circuits. Several of these concepts were investigated using a high-speed chip-to-chip optical interconnect demonstration link. The link employs a modelocked laser and surface-normal optoelectronic modulators that were flip-chip bonded to silicon CMOS circuits. This paper outlines experiments that were performed on or simulated for the link, and discusses the important benefits of ultrashort optical pulses for optical interconnection.

Use of a dielectric stack as a one-dimensional photonic crystal for wavelength demultiplexing by beam shifting

We demonstrate the use of a 30-period dielectric stack structure as a highly dispersive device to spatially separate two beams with a 4-nm wavelength difference by more than their beam width. Unlike previous devices, our structure is simple to fabricate and relatively compact. We discuss possible applications of our device within wavelength-division multiplexing systems.

Skew and jitter removal using short optical pulses for optical interconnection

We demonstrate data resynchronization in a multichannel chip-to-chip free-space optical interconnect for complementary metal-oxide-semiconductor (CMOS) using short optical pulses. Operation of the system is shown at speeds of 82 Mb/s per channel, limited by the repetition rate of the mode-locked laser used. We show explicitly the ability to resynchronize parallel channels and eliminate timing fluctuations; we remove up to /spl plusmn/3/8 of a bit period of interchannel skew and single channel jitter from the transmitted signals in a complete interconnect link that includes optical transmission, reception, and retransmission of digital data.

Wavelength division multiplexed optical interconnect using short pulses

We demonstrate operation of a wavelength division multiplexed chip-to-chip optical interconnect using surface-normal electroabsorption modulators, and a modelocked laser as a single broadband source. The link was successfully operated at 80 Mb/s. While this rate was limited by the repetition rate of the modelocked source, individual CMOS circuits and optoelectronic devices have been shown to work at data rates approaching 1 Gb/s.

Latency reduction in optical interconnects using short optical pulses

We present a new method of latency reduction in optical interconnects: using very low duty cycle return-to-zero encoding (i.e., subpicosecond pulses). An analytical comparison of three different receiver architectures, including transimpedance, integrating, and totem-pole diode pair, is presented. For all three receivers, we demonstrate that using short pulses instead of nonreturn-to-zero (NRZ) shortens the circuit delay. We also experimentally demonstrate a /spl sim/65% reduction in latency of a transimpedance receiver by using short optical pulses. Finally, we show that the latency of optical interconnects can be comparable to or even less than electrical interconnects for global on-chip communication.

Optical pump-probe measurements of the latency of silicon CMOS optical interconnects

We present the first measurements of optical-electrical-optical conversion latency in a hybridly-integrated optoelectronic/silicon complementary metal-oxide-semiconductor (CMOS) chip designed for optical interconnection. Using an optical pump-probe technique, we perform precise measurements with picosecond resolution that closely match our simulations. Our findings suggest that optical interconnects have the potential to provide equal or lower latency than on-chip global wires in future CMOS microelectronics.

Performance enhancement of an optical interconnect using short pulses from a modelocked diode laser

Summary form only given. We have demonstrated a short-pulse optical interconnect that uses a practical, high-repetition-rate modelocked source. BER measurements show that operation with short pulses improves system performance by providing a receiver sensitivity enhancement of 3.3 dB. The link has additional benefits related to timing issues and latency reduction.

Demonstration of a wavelength division multiplexed chip-to-chip optical interconnect

Summary from only given. We have demonstrated operation of a wavelength-division multiplexed optical interconnect using a broadband source. The system data rate of 80 Mb/s is limited by the repetition rate of the laser, but the individual circuits and optoelectronic devices have been shown to work at data rates approaching 1 Gb/s. Such a system has many potential advantages for future short-distance optical interconnects.

Optical interconnects using short optical pulses

We demonstrate the use of a modulator-driven chip-to-chip optical interconnect using short optical pulses to remove jitter and skew. When employing a short (sub-picosecond) pulse laser for optical interconnection, we can use two different aspects of the laser output to our advantage. First, the short pulse duration allows us to sample the data on the output modulators instantaneously, enabling the removal of jitter in output data streams and the removal of inter-channel skew at the modulators. Second, the low jitter output from the laser provides a low jitter signal for clock distribution and, provided the data are also transmitted optically, enables easy synchronization between clock and data.

Optical interconnect operation with high noise immunity

Summary from only given. We demonstrate the operation of a link with high immunity to supply and substrate noise. A total link power penalty of only 0.12 dB/ 100 mV of receiver supply noise was observed. Link performance was unaffected by substrate noise injection from a voltage controlled oscillator (VCO). This high immunity can be attributed to the differential nature of the receiver. The effect of supply noise and crosstalk on electrically single-ended receivers has been studied. To the best of our knowledge, however, this is the first demonstration of the operation of an entire chip-to-chip optical link with modulators and electrically differential receivers quantifying the effect of supply and substrate noise.